Metal etch system

ABSTRACT

Embodiments of systems and methods of etching material from the surface of a wafer are provided. In one representative embodiment, an apparatus comprises a fluid reservoir configured to receive a fluid including an etchant and one or more wafers in a cassette. The apparatus can further comprise a roller member in the fluid reservoir to frictionally engage the one or more wafers and to displace the one or more wafers with respect to a bottom portion of the cassette when the cassette is in the fluid reservoir. The apparatus can further comprise a motor outside the fluid reservoir and magnetically coupled to the roller member such that activation of the motor causes corresponding rotation of the roller member, and thereby rotation of the one or more wafers when the roller member is in frictional engagement with the one or more wafers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/508,648, filed Oct. 7, 2014, which claims the benefit of U.S.Provisional Patent Application No. 61/927,027, filed Jan. 14, 2014, bothof which are incorporated herein by reference in their entirety.

FIELD

The present disclosure is directed to the field of metal etchingsystems, and in particular to improved wet-etching systems.

BACKGROUND

Wet-etching can refer to the use of chemical baths to dissolve portionsof a metal layer situated on a wafer. Wet-etching techniques are oftensimpler and less expensive than dry-etching or de-plating techniques,but can be highly isotropic, which can amplify surface irregularities onthe wafers. Conventional wet-etching systems also typically suffer frompoor chemical usage owing to the boundary layer established between thewafer surface and the chemical bath, which tends to restrict both theflow of spent etchant away from the wafer surface and the flow of freshetchant against the wafer surface. Further, the cassettes or cassettesin which wafers are situated when in the chemical bath can restrict theflow of etchant against certain regions of the wafer surface, causingthose regions to etch at different rates than other regions of the wafersurface. Accordingly, improvements to wet-etching systems are desirable.

SUMMARY

Certain embodiments of the disclosure concern systems and methods ofetching material from the surface of a wafer. In one representativeembodiment, an apparatus comprises a fluid reservoir configured toreceive a fluid including an etchant and one or more wafers situated ina cassette. The apparatus further comprises a roller member situated inthe fluid reservoir to frictionally engage the one or more wafers whenthe cassette is in the fluid reservoir. The apparatus further comprisesa motor situated outside the fluid reservoir and coupled to the rollermember such that rotation of the motor causes corresponding rotation ofthe roller member, and thereby rotation of the one or more wafers whenthe roller member is in frictional engagement with the one or morewafers. The one or more wafers can be displaced with respect to a bottomportion of the cassette when the cassette is in the fluid reservoir.

In another representative embodiment, an apparatus comprises a fluidreservoir configured to receive a fluid including an etchant and acassette configured to receive one or more wafers, and a roller memberin the fluid reservoir to frictionally engage the one or more waferswhen the cassette is in the fluid reservoir. The apparatus furthercomprises a motor situated outside the fluid reservoir and coupled tothe roller member such that activation of the motor causes correspondingrotation of the roller member and rotation of the one or more waferswhen the roller member is in frictional engagement with the one or morewafers, and a fluid agitator in fluid communication with the fluidreservoir to introduce bubbles into the fluid when the fluid is in thefluid reservoir.

In another representative embodiment, a method comprises positioning acassette including one or more wafers situated therein in a fluidreservoir containing a fluid, displacing the one or more wafers from abottom portion of the cassette, rotating the one or more wafers in thecassette, and bubbling a gas through the fluid in the fluid reservoirsuch that bubbles pass through the cassette.

In another representative embodiment, an apparatus comprises a fluidreservoir configured to receive one or more wafers in a cassette, and aroller member situated in the fluid reservoir to frictionally engage theone or more wafers when the cassette is in the fluid reservoir. Theroller member can further displace the one or more wafers with respectto a bottom portion of the cassette such that the one or more wafers canbe rotated by the roller within the cassette while simultaneously beingdisplaced from the bottom of the cassette. The apparatus can furthercomprise a motor situated outside the fluid reservoir and magneticallycoupled to the roller member such that rotation of the motor causescorresponding rotation of the roller member, and thereby rotation of theone or more wafers within the cassette when the cassette is in the fluidreservoir. The apparatus can further comprise a fluid agitator in fluidcommunication with the fluid reservoir to introduce gas bubbles of apredetermined size into a fluid when the fluid is received by the fluidreservoir, and one or more bubble guide members to guide gas bubblesintroduced into the fluid by the fluid agitator into the cassette atparticular angles and particular directions.

The foregoing and other objects, features, and advantages of thedisclosure will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a representative embodiment ofa wet-etching system with a front panel removed for purposes ofillustration.

FIG. 2 illustrates a perspective view of a representative embodiment ofa fluid reservoir assembly.

FIG. 3 illustrates a cross-sectional side elevation view of the fluidreservoir assembly of FIG. 2 taken along line 3-3 of FIG. 2.

FIG. 4 illustrates a cross-sectional view of the fluid reservoirassembly of FIG. 2 taken along line 4-4 of FIG. 2.

FIG. 5 illustrates a perspective view of a representative embodiment ofa fluid agitator.

FIG. 6 illustrates a perspective view of the underside of the fluidagitator of FIG. 5.

FIG. 7 illustrates a partially exploded view the fluid agitator assemblyof FIG. 5.

FIG. 8 illustrates an exploded view of the main body portion of thefluid agitator of FIG. 5.

FIG. 9 illustrates cross-sectional view of the fluid agitator of FIG. 5.

FIG. 10 is a cross-sectional view of the fluid reservoir assembly ofFIG. 2 in operation.

FIG. 11 is a schematic illustration of a representative embodiment of agas supply system.

FIG. 12 is a plan view of a plurality of wafers illustrating relativesurface uniformity of the wafers.

FIG. 13 illustrates a computer simulation of flow velocities of a fluidthrough a fluid reservoir assembly similar to the fluid reservoirassembly of FIG. 2.

FIG. 14 illustrates a wafer processed in the fluid reservoir assembly ofFIG. 13.

FIG. 15 is a chart illustrating certain embodiments'within-wafer-uniformity values for wafers placed in slots 1-25 of acassette before and after processing in a fluid reservoir assembly.

FIG. 16 is a cross-sectional view of a wafer illustrating representativefeatures on the wafer surface that may be processed with the fluidreservoir assembly of FIG. 2.

DETAILED DESCRIPTION

For purposes of this description, certain aspects, advantages, and novelfeatures of the embodiments of this disclosure are described herein. Thedisclosed methods, apparatus, and systems should not be construed asbeing limiting in any way. Instead, the present disclosure is directedtoward all novel and nonobvious features and aspects of the variousdisclosed embodiments, alone and in various combinations andsub-combinations with one another. The methods, apparatus, and systemsare not limited to any specific aspect or feature or combinationthereof, nor do the disclosed embodiments require that any one or morespecific advantages be present or problems be solved.

Although the operations of some of the disclosed embodiments aredescribed in a particular, sequential order for convenient presentation,it should be understood that this manner of description encompassesrearrangement, unless a particular ordering is required by specificlanguage set forth below. For example, operations described sequentiallymay in some cases be rearranged or performed concurrently. Moreover, forthe sake of simplicity, the attached figures may not show the variousways in which the disclosed methods can be used in conjunction withother methods. Additionally, the description sometimes uses terms like“provide” or “achieve” to describe the disclosed methods. These termsare high-level abstractions of the actual operations that are performed.The actual operations that correspond to these terms may vary dependingon the particular implementation and are readily discernible by one ofordinary skill in the art.

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the terms “coupled” and “associated” generally meanelectrically, electromagnetically, and/or physically (e.g., mechanicallyor chemically) coupled or linked and does not exclude the presence ofintermediate elements between the coupled or associated items absentspecific contrary language.

In some examples, values, procedures, or apparatus may be referred to as“lowest,” “best,” “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyalternatives can be made, and such selections need not be better,smaller, or otherwise preferable to other selections.

In the following description, certain terms may be used such as “up,”“down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” andthe like. These terms are used, where applicable, to provide someclarity of description when dealing with relative relationships. But,these terms are not intended to imply absolute relationships, positions,and/or orientations. For example, with respect to an object, an “upper”surface can become a “lower” surface simply by turning the object over.Nevertheless, it is still the same object. If allowed, fluids generallyflow under gravity toward the bottom of a system and gases within thefluid generally flow through the fluid toward the top of the system.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andmaterials are described below. The materials, methods, and examples areillustrative only and not intended to be limiting. Other features of thedisclosure are apparent from the following detailed description and theclaims.

Unless otherwise indicated, all numbers expressing quantities ofcomponents, molecular weights, percentages, temperatures, times, and soforth, as used in the specification or claims are to be understood asbeing modified by the term “about.” Accordingly, unless otherwiseindicated, implicitly or explicitly, the numerical parameters set forthare approximations that can depend on the desired properties soughtand/or limits of detection under standard test conditions/methods asunderstood by those of ordinary skill in the art. When directly andexplicitly distinguishing embodiments from discussed prior art, theembodiment numbers are not approximates unless the word “about” isrecited. Furthermore, not all alternatives recited herein areequivalents unless expressly stated otherwise.

The systems, methods and devices disclosed herein can be used insemiconductor wafer fabrication processes such as material-etchingprocesses. Etching can refer to the process of removing material, suchas metal, from the surface of a wafer, and can be used to pattern filmson the wafer to form desired features (e.g., conductive pathways,interconnects, etc.). The systems, methods, and devices disclosed hereincan be used to significantly improve wet-etch processing and, thus, canoffer high-quality etching at much lower prices than other etchingtechniques, such as dry-etching or de-plating systems. For example,certain embodiments of the systems, methods, and devices disclosedherein are capable of providing greatly improved within-wafer (WIW)uniformity, such as WIW uniformities below 5% and, in some cases, lessthan 2% for a 200 mm wafer. As used herein, the term “within-waferuniformity” (“WIW”) refers to a measure of the planarization of thesurface of a wafer, and is typically expressed as a percentage by whichthe thickness of a material at various points on the wafer surfacevaries with respect to a median value. Within-wafer uniformity can bedetermined using, for example, any of various multipoint probe metrologysystems to measure electrical resistance of a wafer surface before andafter processing by a wet-etching system. The electrical resistancevalues can then be used in combination with parameters such as etchrate, material thickness, etc., to determine the relative consistency ofmaterial removal at various locations on the wafer surface by thewet-etching system.

Referring to wet-etch systems generally, the systems disclosed hereincan include one or more fluid reservoirs configured to receive aplurality of wafers in a cassette, and can include one or more inletsthrough which an etching fluid can be provided. The fluid reservoir canbe configured such that the fluid can be introduced at a bottom endportion of the fluid reservoir and flow upward through the fluidreservoir around the wafers to a top end portion of the fluid reservoir.As the fluid flows past the wafers, the etchant can etch material fromone or more surfaces of the wafers.

In certain embodiments of the disclosed apparatus, the fluid reservoirfurther includes a fluid agitator situated below the wafers andconfigured to agitate the fluid during material-etching processes by,for example, introducing gas bubbles into the fluid. The gas bubbles actto mix the fluid in the reservoir to help ensure a uniform concentrationof etchants throughout the volume of fluid, as well as to disrupt theformation of fluid boundary layers near the wafer surfaces such that theentire wafer surface is exposed to etchant. This can improve surfaceuniformity as well as promote a consistent etch rate both with respectto different regions of the surface of a single wafer, and betweendifferent wafers in the cassette by facilitating the movement ofdepleted etchant and etched material away from the wafer surface and themovement of fresh etchant against the wafer surface. Additionally, thefluid agitator can be configured to vary the frequency and/or size ofbubbles generated at a plurality of predetermined regions within thefluid reservoir corresponding to different portions of the wafers tofurther improve etching uniformity.

The fluid reservoir can also include a motor situated outside the fluidreservoir and a roller member situated within the fluid reservoirconfigured to cause rotation of the wafers in the cassette. Rotation ofthe wafers in the cassette during metal-etching processes can furtherimprove the uniformity and consistency of etching. In some cases, themotor can be coupled to the roller assembly magnetically, such that themotor is not in contact with the fluid in the fluid reservoir, which canreduce exposure of the motor components to corrosive etchant fluids.

In some embodiments, the cassette can be movable between a raisedposition and lowered position to selectively situate the plurality ofwafers in the fluid reservoir. The cassette can also be configured suchthat when the cassette is in the fluid reservoir, the roller memberengages the wafers to displace the wafers above a bottom portion of thecassette so as to reduce interference in the etching process caused byproximity of the cassette structure to the wafers. Representativeembodiments of a fluid reservoir, a cassette, a roller member, and amotor are further described below. It has been found that rotation ofthe wafers while simultaneously displacing the wafers from the bottomportion of the cassette during etching act synergistically to provideimproved wafer surface uniformity as compared to conventionalwet-etching techniques.

It has also been found that agitating the fluid by introducing bubblesof an inert gas into different regions of the fluid reservoir atdifferent rates, rotation of the wafers, and displacement of the wafersrelative to the cassette also act synergistically to providesurprisingly superior wafer surface uniformity during etching processesas compared to conventional wet-etching techniques. Additionally,certain embodiments of the systems described herein can be lessexpensive, more compact, and/or easier to maintain than conventionalwet-etching systems. Certain embodiments of the disclosed systems reducethe quantity of etchant chemicals required, provide greater throughput,and/or eliminate processing steps relative to conventional etchingsystems.

EXAMPLE 1 Representative Wet-Etching System

FIG. 1 illustrates a perspective view of a representative embodiment ofa wet-etching system 100 (also referred to as a “wet-etching tool”),including an outer housing or enclosure 102. The enclosure 102 caninclude first and second side walls 114, a rear portion 118, a hood 120,a floor 122, and, if desired, a plurality of wheels 124. The system 100can also include a first fluid reservoir assembly 104, a second fluidreservoir assembly 106, a rinse tank or reservoir 108, and a robotic armor manipulator 110. In the embodiment shown, the first and second fluidreservoir assemblies 104, 106 can be mounted on the sidewalls 114, suchas on mounting tracks 116. The manipulator 110 can be used to move ormanipulate a cassette 112 (also referred to as a “cassette”) among thefirst and second fluid reservoir assemblies 104, 106, and the rinse tank108. The cassette 112 can be configured to receive one or moresemiconductor wafers illustrated schematically at 126, and can belowered into the first reservoir assembly 104, the second reservoirassembly 106, and/or the rinse tank 108 by the manipulator 110.

EXAMPLE 2 Representative Fluid Reservoir Assembly

FIG. 2 illustrates a perspective view of a representative embodiment ofa fluid reservoir assembly 200 that can be used in combination with thewet-etching system 100 as, for example, fluid reservoir assemblies 104and/or 106. The fluid reservoir assembly 200 can include a substantiallyrectangular tank or fluid reservoir 202, a roller member 204 situated inthe fluid reservoir 202, and a fluid agitator 206 situated beneath theroller member 204. The fluid reservoir assembly 200 can also include amotor 208 situated outside the fluid reservoir 202 and coupled to theroller member 204. In some embodiments, the fluid reservoir assembly 200can be a discrete unit such that any suitable number of fluid reservoirassemblies can be incorporated into a wet-etching system, such as thesystem 100 of FIG. 1.

The fluid reservoir 202 can have an upper portion 203 and a lowerportion 205, and can be configured to receive a fluid including one ormore etchants (for example, for processing semiconductor wafers) via oneor more inlet ports 246 in fluid communication with the lower portion205 of the fluid reservoir 202. In some embodiments, the upper portion203 of the fluid reservoir 202 can be notched to allow controlledoverflow of fluid out of the fluid reservoir 202 when, for example, acassette is in the fluid reservoir 202. The fluid reservoir 202 can alsoinclude an overflow collection enclosure 248 (indicated in phantom),which can be configured to receive fluid that overflows the fluidreservoir 202, and to direct the fluid toward a port 250 locatedadjacent the lower portion 205 of the fluid reservoir 202. In someembodiments, the port 250 can be in communication with a recirculationpump, which can recirculate the fluid back into the fluid reservoir 202.The fluid reservoir 202 can further include a drain 207 situated in thelower portion 205 of the fluid reservoir 202 for draining fluid directlyfrom the fluid reservoir 202.

Each of the inlet ports 246 can be in fluid communication with arespective diffuser chamber, such as the diffuser chamber 252 shown inFIG. 2. Referring specifically to the diffuser chamber 252 for purposesof illustration, the diffuser chamber 252 can be mounted adjacent thelower portion 205 of the fluid reservoir 202, and can include aplurality of diffuser openings 254 defined therein along a portion ofthe length of the diffuser chamber 252. The diffuser openings 254 can bein fluid communication with the interior of the fluid reservoir 202 suchthat a fluid can be supplied to the diffuser chamber 252 via the inlet246, and thereby diffused into the fluid reservoir 202 in a controlledmanner via the plurality of diffuser openings 254. This can help topromote, for example, even distribution of fluid into the fluidreservoir 202 and, thereby a uniform concentration of etchantsthroughout the volume of the fluid reservoir 202. In operation, fluidcan be diffused into the lower portion 205 of the fluid reservoir 202via the diffuser chamber 252, and can flow upwardly toward the upperportion 203 of the fluid reservoir 202. Excess fluid can flow over theupper portion 203 of the fluid reservoir 202, and can be collected bythe overflow collection enclosure 248 for recirculation via the port250.

Referring to FIGS. 2 and 3, the fluid reservoir 202 can be configured toreceive a cassette 210, which can be movable between a raised position,in which the cassette 210 is positioned above the fluid reservoir 202(see, e.g., cassette 112 of FIG. 1), and a lowered position, in whichthe cassette 210 is in the fluid reservoir 202 and, thereby, immersed inthe fluid contained in the reservoir 202 (see FIG. 2). The cassette 210can include side walls 212 and a bottom portion 214, and can beconfigured to receive a plurality of wafers 216. To that end, the sidewalls 212 can include a plurality of slots 218 (FIG. 3) configured suchthat when the wafers 216 are received in the slots 218, the wafers 216can be situated parallel to and spaced apart from one another in anupright configuration in the cassette 210. The side walls 212 and thebottom portion 214 can also be contoured such that a curvature of theside walls 210 and the bottom portion 212 approximates a curvature ofthe wafers 216, allowing a perimeter or edge portion 222 of the wafers216 to contact the side walls 212 and/or the bottom portion 214 when thewafers 216 are received in the cassette 210.

Referring to FIGS. 2, 3, and 4, the bottom portion 214 of the cassette210 can define an opening generally indicated at 220. In the embodimentshown, the opening 220 can extend along the length of the cassette 210,and can allow fluid to flow into the cassette 210 as the cassette 210 islowered into the fluid reservoir 202. The opening 220 can also beconfigured such that the edge portion 222 of each of the respectivewafers 216 is accessible via the opening 220 to allow the roller member204 to contact the edge portions 222 of the wafers 216, as furtherdescribed below.

Referring to FIG. 3, the roller member 204 can extend along the lengthof the fluid reservoir 202 such that a longitudinal axis 228 of theroller member 204 is oriented perpendicular to the wafers 216 in thecassette 210. The roller member 204 can be coupled at one end to a motor224, and to a bearing 226 supported by a fixture 227 at the opposite endof the fluid reservoir 202 from the motor 224. In this manner, theroller member 204 can be rotated within the fluid reservoir 202 by themotor 224. In some embodiments, the roller member 204 can be supportedat one or both ends by spherical bearings, which can reduce the requireddegree of alignment precision and wear of rotating parts.

In some embodiments, the roller member 204 can be mounted in the fluidreservoir 202 such that as the cassette 210 is lowered into the fluidreservoir 202, the roller member 204 can pass through the opening 220 inthe cassette 210 and contact the edge portions 222 of the wafers 216,thereby displacing (e.g., lifting) the wafers 216 a distance D from thebottom portion 214 of the cassette 210, as shown in FIG. 4. In otherwords, the cassette 210 can be situated in the fluid reservoir 202 suchthat the edge portions 222 of the wafers 216 contact the roller member204 and are lifted off of the bottom portion 214 of the cassette 210 adistance D as the cassette 210 is lowered into the fluid reservoir 202.This can allow greater fluid flow around the edges of the wafers 216during processing, which can help to minimize the shadowing effectcaused by proximity of the cassette 210 to certain portions of thewafers 216.

In some embodiments, the distance D can be a proportion of the diameterof the wafers 216. For example, in some embodiments, the distance D canbe 5% of the diameter of the wafers 216, 10% of the diameter of thewafers 216, 15% of the diameter of the wafers 216, etc. In someembodiments, the distance D can be related to the diameter of the rollermember 204. For example, in some embodiments, the distance D can be 50%of the diameter of the roller member 204. In some embodiments, thedistance D can be a specific measurement regardless of the size of thewafers, such as one to two inches.

In some embodiments, the wafers 216 need not be displaced from thebottom portion 214 of the cassette 210 by the roller member 204, but maybe displaced by any other suitable member or structure located inside oroutside the cassette 210. For example, the wafers 216 can be displacedby a displacement mechanism or member indicated in phantom at 221 thatis separate from the roller member 204 and configured to displace thewafers 216 with respect to the bottom portion 214 of the cassette 210.In some embodiments, the displacement member 221 can be configured todisplace the wafers 216 when the wafers 216 are not being rotated by theroller member 204. In some embodiments, the displacement member 221 canbe configured to displace the wafers 216 from the bottom portion 214 ofthe cassette 210 while the wafers 216 are being rotated by the rollermember 204. In some embodiments, the roller member 204 can displace thewafers 216, and the manipulator 110 can be configured to rotate thewafers 216 or otherwise move the wafers 216 in the fluid within thefluid reservoir 202.

Referring again to FIG. 3, the motor 224 can be housed in a motorhousing 230 mounted on the exterior of the fluid reservoir 202, and canbe coupled to a driving hub 232 via an output shaft 234. The driving hub232 can be situated in a mounting plate 236, which can be sealinglyreceived in an opening 238 in the fluid reservoir 202. As shown in FIG.3, the driving hub 232 and a driven hub 242 coupled to the roller member204 can each include a plurality of magnet elements 244 situatedopposite one another across the mounting plate 236. The respectivemagnet elements 244 of the driving hub 232 and the driven hub 242 can bespaced apart from and magnetically coupled to one another across themounting plate 236 such that rotation of the driving hub 232 (forexample, by the motor 224) causes corresponding rotation of the drivenhub 242 and, hence, of the roller member 204 about its longitudinal axis228. In some embodiments, the driven hub 242 can be supported by, and/orrotate about, a protrusion in the wall of the fluid reservoir 202.

In this manner, the roller member 204 can be rotated within the fluidreservoir 202 without the need for a direct mechanical linkage betweenthe roller member 204 and the motor 224. This can reduce the risk ofleakage by eliminating leak-prone sealing elements required to sealshafts or other torque transfer mechanisms across the wall of the fluidreservoir 202, and can reduce the introduction of contaminants andparticulates into the fluid reservoir caused by, for example, wear ofmoving parts, leakage of lubricants from bearings, etc. However, inalternative embodiments, the roller assembly 204 may be mechanicallylinked across the wall of the fluid reservoir. In further alternativeembodiments, the roller assembly 204 can be rotated by, for example, astator situated outside the fluid reservoir 202 and configured to rotatea rotor situated inside the fluid reservoir via a changing magneticfield produced by the stator.

Referring again to FIGS. 2 and 3, the fluid agitator 206 can be situatedin the lower portion 205 of the fluid reservoir 202, and can beconfigured to agitate the fluid in the fluid reservoir by introducinggas bubbles of an inert gas (for example, nitrogen) into the fluid in acontrolled manner, as further described below. In the embodiment shown,the fluid agitator 206 can be situated on support members 209 (see,e.g., FIGS. 3 and 4) such that fluid agitator 206 is spaced apart fromthe bottom of the fluid reservoir 202. The fluid agitator 206 can alsobe located such that when the cassette 210 is in the fluid reservoir202, the cassette 210 is positioned above the fluid agitator 206 andspaced apart from the fluid agitator 206 by one or more bubble guidemembers 256, as shown in FIGS. 4 and 5.

Referring to the bubble guide members 256 in more detail, the fluidreservoir assembly 200 can include two bubble guide members 256 situatedin the fluid reservoir 202 to guide gas bubbles introduced into thefluid by the fluid agitator 206 into the cassette 210. In the embodimentshown, the bubble guide members 256 can be situated near the edges of atop plate 264 of the fluid agitator 206, and can be coupled to the fluidagitator 206 in a rigid manner. For example, in the embodiment shown,the bubble guide members 256 can be coupled to the fluid agitator 206 bya plurality of fasteners 257 configured to be received in a plurality ofrespective fastener openings 259. The bubble guide members 256 caninclude respective upper portions 258 and lower portions 260. In theembodiment shown, the lower portions 258 can comprise two extensions,which can be received in openings 261 defined in the fluid agitator 206.

The upper portions 258 can be configured to contact the cassette 210when the cassette 210 is in the fluid reservoir 202, as shown in FIG. 4.In this manner, the bubble guide members 256 can restrict furthermovement of the cassette 210 when the cassette 210 is lowered into thefluid reservoir 202 such that the cassette 210 is suspended above thefluid agitator 206. Furthermore, the bubble guide members 256 can guidegas bubbles introduced into the fluid by the fluid agitator 206 into thecassette 210 such that gas bubbles are substantially prevented fromtraveling around the outside of the cassette 210 when the cassette 210is situated on the upper portions 258 of the bubble guide members 256.In this manner, the gas bubbles can be guided into the cassette 210 viathe opening 220, as shown in FIG. 10, which can allow the bubbles tolocally mix (i.e., agitate) the fluid adjacent the wafers 216 such thatfresh etchant can flow against the surfaces of the wafers 216 and spentetchant can flow away from the surfaces of the wafers 216. This can helpto stir or agitate the boundary layer proximate the surfaces of thewafers 216, which can improve etch rate and uniformity across the wafersurface.

Referring to FIG. 5, the bubble guide members 256 can each define one ormore guide member openings 262. The guide member openings 262 can belocated on the respective lower portions 260 of the bubble guide members256 such that when the bubble guide members 256 are coupled to the fluidagitator 206, the guide member openings 262 are substantially alignedwith the diffuser openings 254 of the diffuser chamber 252. In thismanner, fluid flowing into the fluid reservoir 202 from the diffuseropenings 254 can pass through the guide member openings 262, and flowupwardly across the wafers 216 in the cassette 210 toward the top of thefluid reservoir 202.

The fluid agitator 206 can include a main body portion 268, with the topplate 264 situated on top of the main body portion 268. The top plate264 can include a plurality of fluid agitator regions defined on thesurface of the top plate 264, such as the fluid agitator regions266A-266C illustrated in FIG. 5. The fluid agitator regions 266A-266Ccan be rectangularly-shaped, and can extend along a length of the fluidagitator 206. In some embodiments, the fluid agitator regions 266A-266Ccan have a length corresponding to a length of the cassette 210, and canbe configured to agitate the fluid proximate the wafers 216 byintroducing gas bubbles into the fluid such that the gas bubbles flowinto the cassette 210 when the cassette 210 is in the fluid reservoir202. In some embodiments, the fluid agitator regions 266A-266C can bespaced apart from one another such that bubbles generated by eachrespective fluid agitator region 266A-266C flow into different portionsof the cassette 210 and/or adjacent different regions of the wafers 216,as further described below. In some embodiments, the fluid agitatorregions 266A-266C can be configured to agitate the fluid at differentrates by introducing bubbles into the fluid at different rates. This canallow the rate at which material is etched from different regions of thewafer surfaces to be controlled according to their location in the fluidreservoir 202 with respect to the fluid agitator regions 266A-266C. Inalternative embodiments, the fluid agitator 206 can include any suitablenumber of fluid agitator regions having any suitable shape and/ororientation.

Each of the fluid agitator regions 266A-266C can include a plurality offluid agitator openings 270 defined in the top plate 264. The fluidagitator openings 270 can be configured to introduce gas bubbles of apredetermined size into the fluid in the fluid reservoir 202. In someembodiments, the fluid agitator openings 270 can have respectivediameters of from 0.01 to 0.2 inch, and can introduce gas bubbles havingcorresponding diameters into the fluid. In some embodiments, the fluidagitator openings 270 can have a diameter of from 0.04 inch to 0.12 inchsuch that they can produce gas bubbles having a diameter of from 0.04inch to 0.12 inch. In some embodiments, the fluid agitator openings 270can have a diameter of 0.03 inch such that the openings introducebubbles into the fluid having a diameter of 0.03 inch. In this manner,the bubble introduce regions 266A-266C can introduce gas bubbles intothe fluid having a greater degree of size uniformity than is possible byother methods, such as passing gas through a porous membrane directlyinto the fluid.

In alternative embodiments, the fluid agitator openings 270 can have anysuitable diameter, and the diameter of the fluid agitator openings 270can differ among the fluid agitator regions 266A-266C. In furtheralternative embodiments, the diameter of the different fluid agitatoropenings 270 can differ within each fluid agitator region 266A-266C, asdesired.

In the embodiment shown, the fluid agitator openings 270 can be arrangedin rows with substantially equal spacing between respective openings. Inthis manner, gas bubbles introduced into the fluid by the openings canbe spaced apart from one another at about the same distance as theopenings 270 from which they originate. This can result in asubstantially uniform density of gas bubbles in the fluid adjacent eachrespective fluid agitator region 266A-266C. Alternatively, the fluidagitator openings 270 can have any suitable spacing within the fluidagitator regions 266A-266C, can be arranged in any suitable pattern, orcan be arranged at random, depending upon the desired processcharacteristics.

Referring still to FIG. 5, the fluid reservoir assembly 200 can includea plurality of conduits to supply gas to the fluid agitator 206. In theembodiment shown, the fluid reservoir 200 can include a first set of gassupply conduits 272A-272C, and a second set of gas supply conduits274A-274C configured to provide a supply of an inert gas (for example,nitrogen gas) at a predetermined pressure to the fluid agitator regions266A-266C. The fluid reservoir assembly 200 can also include a set offluid evacuation conduits 276A-276C, which can be situated between thefirst and second sets of gas supply conduits 272A-272C and 274A-274C,and can be configured to evacuate fluid from the main body portion 268of the fluid agitator 206, as further described below. In the embodimentshown, the first and second sets of gas supply conduits 272A-272C,274A-274C, and the fluid evacuation conduits 276A-276C, can be shapedsuch that the respective conduits extend from the underside of the fluidagitator 206, upwardly through the fluid reservoir 202, and outwardlythrough the upper portion 203 of the fluid reservoir 202 to connectionpoints external to the fluid reservoir assembly 200 (see, e.g., FIG. 4).

FIG. 6 illustrates the respective connection points of the first andsecond sets of gas supply conduits 272A-272C, 274A-274C, and the fluidevacuation conduits 276A-276C on the underside of the fluid agitator206. In the embodiment shown, the first set of gas supply conduits272A-272C can be fluidly coupled to one side of the main body portion268 of the fluid agitator 206 at locations corresponding to the fluidagitator regions 266A-266C, respectively. In other words, the gas supplyconduit 272A can be coupled to the underside of the fluid agitator 206opposite the fluid agitator region 266A, the gas supply conduit 272B canbe coupled to the fluid agitator 206 opposite the fluid agitator region266B, and the gas supply conduit 272C can be coupled to the fluidagitator 206 opposite the fluid agitator region 266C.

In an analogous manner, the second set of gas supply conduits 274A-274Ccan be fluidly coupled to the opposite side of the main body portion 268of the fluid agitator 206 from the first set of gas supply conduits272A-272C at respective locations corresponding to the fluid agitatorregions 266A-266C. In other words, the gas supply conduit 274A can becoupled to the underside of the fluid agitator 206 opposite the fluidagitator region 266A, the gas supply conduit 274B can be coupled to thefluid agitator 206 opposite the fluid agitator region 266B, and the gassupply conduit 274C can be coupled to the fluid agitator 206 oppositethe fluid agitator region 266C. In this manner, each of the fluidagitator regions 266A-266C can coupled to respective first and secondgas supply conduit 272A-272C, 274A-274C, and can receive gas suppliedtherefrom, as further described below. However, in alternativeembodiments, the fluid agitator 206 can include any suitable number ofgas supply conduits and/or fluid evacuation conduits, which can becoupled to the fluid agitator 206 at any suitable location, as desired.

FIGS. 7 and 8 illustrate exploded views of the fluid agitator 206 atvarying levels of detail. FIG. 7 illustrates the main body portion 268of the fluid agitator 206 separated from the top plate 264, andillustrates a sealing member 278 configured to be situated between thetop plate 264 and a porous membrane 280 of the main body portion 268.The sealing member 278 can be configured to reduce leakage of fluid pastthe top plate 264 into the main body portion 268 when fluid is receivedin the fluid reservoir 202.

FIG. 8 illustrates an exploded view of the main body portion 268 of thefluid agitator 206. The main body portion 268 can include three recesseswhich, when covered by the porous membrane 280, can define threechambers 282A-282C corresponding to the three fluid agitator regions266A-266C. The three chambers 282A-282C can be separated by respectivedivider members 284, 286, and can be sealed from one another and fromthe porous membrane 280 by respective sealing members 288A-288C. Thechambers 282A-282C can define respective channels 290A-290C, which canextend along the length of the chambers 282A-282C, and can collect anyfluid that leaks into the chambers 282A-282C past the sealing members288A-288C and/or the sealing member 278.

Each of the chambers 280A-280C can include respective drain openings 291defined near the centers of the respective channels 290A-290C. Thechannels 290A-290C can be sloped or graded such that any fluid thatleaks into the chambers 282A-282C is induced to flow along therespective channels 290A-290C toward the drains 291. The respectivedrains 291 of the chambers 282A-282C can be in fluid communication withthe respective fluid evacuation conduits 276A-276C via fittings such asfitting 295 of FIG. 9. In this manner, fluid received into the chambers282A-282C can be evacuated via the respective fluid evacuation conduits276A-276C. Each of the channels 290A-290C can also include a pluralityof side channels 292, which can be configured to drain to the channels290A-290C to facilitate collection and evacuation of fluid from thechannels 290A-290C via the drains 291.

Each of the chambers 282A-282C can also include gas inlet openingscoupled to the respective first and second gas supply conduits272A-272C, 274A-274C. For example, in the embodiment shown, each of thechambers 282A-282C can include respective gas inlet openings 293A-293Cdefined in respective side walls 294A-294C of the chambers 282A-282C.The gas inlet openings 293A-293C can be in fluid communication with thefirst gas supply conduits 272A-272C, respectively, via plenums such asplenum 287 defined in the main body portion 268, as illustrated in FIG.9. The plenums such as plenum 287, in turn, can be in communication withfittings such as fitting 296 illustrated in cross-section in FIG. 9.Each of the chambers 282A-282C can also include analogous gas inletopenings defined in side walls opposite the side walls 294A-294C, suchas gas inlet opening 294 illustrated in FIG. 9, which can be in fluidcommunication with the second gas supply conduit 274 b via plenum 289and fitting 297 (see FIG. 9). In this manner, each of the chambers282A-282C can receive gas from respective first and second gas supplyconduits 272A-272C and 274A-274C located at opposite ends of therespective chambers 282A-282C.

The porous membrane 280 can be situated between the chambers 282A-282Cand the top plate 264 of the fluid agitator 206, as shown in FIGS. 7 and8. The porous membrane 280 can be in fluid communication with thechambers 282A-282C and the fluid agitator regions 266A-266C such thatgas can permeate through the porous membrane 280 from the chambers282A-282C to the respective fluid agitator regions 266A-266C, where itcan enter the fluid as gas bubbles via the openings 270. The porousmembrane 280 can cooperate with the sealing members 288A-288C to sealthe respective chambers 282A-282C from one another such that eachchamber 282A-282C can receive gas at a different pressure and/or flowrate. For example, in some embodiments nitrogen gas at 1.0 psi can beintroduced into the first chamber 282A at a rate of 5.5 standard cubicfeet per hour, into the second chamber 282B at a rate of 3 standardcubic feet per hour, and into the third chamber 282C at a rate of 5standard cubic feet per hour. The gas can then permeate through theregions of the porous membrane 280 adjacent the different chambers282A-282C at different rates in accordance with the differing pressuresand/or flow rates within each of the chambers 282A-282C.

In this manner, the fluid agitator regions 266A-266C can introduce gasbubbles into the fluid at different rates corresponding to the differentgas pressures and/or flow rates within the respective chambers282A-282C. The porous membrane 280 can also be configured to regulatethe pressure within respective chambers 282A-282C over the area of theporous membrane 280 adjacent each of the chambers 282A-282C, such thatgas permeates the porous membrane and, hence, bubbles form at therespective fluid agitator regions 266A-266C, at relatively uniform ratesacross the areas of the respective fluid agitator regions 266A-266C. Inthis manner, agitation of the fluid can be precisely controlled suchthat wafers 216 at each position in the cassette 210 experience similarfluid agitation and, thereby, material-etch rates. In some embodiments,the porous membrane 280 can be made from any suitable polymericmaterial, such as PTFE.

Referring to FIG. 10, prior to operation of the fluid reservoir assembly200, a fluid can be introduced into the fluid reservoir 202. Fluid canflow through the inlets 246 into the diffuser chambers 252, as indicatedby arrows 251 and 253, and from the diffuser chambers 252 into the fluidreservoir 202 and through the guide member openings 262 in the bubbleguide members 256, as indicated by arrows 255 and 257. In someembodiments, fluid can be introduced into the fluid reservoir 202 at agenerally constant flow rate during processing such that fluid flowsupwardly through the cassette 210 in the direction of arrows 259, andout of the fluid reservoir 202 into the overflow enclosure 248. Forexample, in some embodiments, fluid can be introduced into the fluidreservoir 202 at a rate of from 10 liters per minute to 40 liters perminute, depending upon factors including the concentration of etchant inthe fluid, the amount of material to be etched, etc.

In some cases, the fluid can include an etchant to etch a metal, such asgold, from the surfaces of the wafers 216. For example, in someembodiments, the fluid can include a mixture of nitric acid andhydrochloric acid in a ratio of 1:3 (sometimes referred to as aquaregia), which can etch gold at a rate of 10 μm/minute at roomtemperature. In some embodiments, the fluid can include a mixture of 1%iodine and 2-3% potassium iodide in a carrier fluid such as water, whichcan etch gold at a rate of 1 μm/minute. In some embodiments, the lengthof processing can be from 1 minute to 20 minutes, depending upon factorssuch as the material to be etched, the concentration of etchant(s) inthe fluid, the temperature of the fluid, and/or the amount of materialto be etched from the wafer surface. In some embodiments, the fluid canbe an aqueous solution of sodium cyanide or potassium cyanide, or anyother suitable etchant, as desired. In some embodiments, the fluid canbe a H₂O₂ solution in a carrier fluid, such as water, and can beconfigured to etch TiW. In some embodiments, the H₂O₂ solution can havea concentration of from 2% to 30%. For example, in some embodiments, thefluid can be a 30% H₂O₂ solution, which can etch TiW at a rate of 5.7A/s at a temperature of 50° C. for a processing time of 8.75 minutes.

Returning to FIG. 10, the cassette 210 containing a plurality of wafers216 loaded into respective slots 218 can be lowered into the fluidreservoir 202 (for example, by the manipulator 110 of FIG. 1) until thecassette 210 contacts the bubble guide members 256. In some embodiments,the cassette 210 can be configured to receive, for example, 25 wafers216, or any other suitable number of wafers 216. In some embodiments,the wafers 216 can have diameters of, for example, 75 mm, 100 mm, 125mm, 200 mm, 300 mm, or any other suitable diameter, and can includelayers or patterned features comprised of material to be etched. In someembodiments, the fluid reservoir 202 can be configured to etch, forexample, palladium, aluminum, copper, molybdenum, rhodium, iridium,silver, copper, nickel, chromium, titanium, tantalum, zirconium,hafnium, niobium, tungsten, silicon, sapphire, or any combinationthereof, from the surface of the wafers 216.

As the cassette 210 is lowered onto the bubble guide members 256, theroller member 204 can pass through the opening 220 in the bottom portion214 of the cassette 210, contact (i.e., frictionally engage) therespective edge portions 222 of the wafers 216, and displace the wafers216 relative to the bottom portion 214 of the cassette 210. With thecassette 210 fully received within the fluid reservoir 202 and restingatop the bubble guide members 256, the wafers 216 can then be rotatedwithin the cassette 210 by rotating the roller member 204 (e.g., byactivating the motor 224), as described above. In the embodiment shown,the wafers 216 are illustrated rotating in a clockwise direction, asindicated by arrow 249. However, it should be understood that the wafers216 can be rotated in either a clockwise direction, a counterclockwisedirection, or both a clockwise and counterclockwise direction duringprocessing, as desired. The wafers 216 can also be rotated continuouslyor intermittently, and may be rotated while displaced from the bottomportion 214 of the cassette 210 or while being only slightly lifted suchthat the wafers are not in contact with the bottom portion 214 and/orthe side walls 212 of the cassette 210, but are not lifted to an extentsuch that the wafers are “displaced” as used herein.

In some embodiments, prior to the introduction of gas into the chambers282A-282C (or after a period of time during which gas is not provided tothe chambers 282A-282C), fluid from the fluid reservoir 202 may leakinto the chambers 282A-282C, and may interfere with the production ofgas bubbles by the fluid agitator 206. Thus, prior to introducing gasinto the fluid in the fluid reservoir 202, gas may be introduced intothe chambers 282A-282C at high pressure for a relatively short durationsuch that any fluid that has accumulated in the chambers 282A-282C canbe evacuated via the respective drains 291 and evacuation conduits276A-276C (see, e.g., FIGS. 5 and 8). With the chambers 282A-282Ccleared of fluid, gas can then be supplied to the respective chambers282A-282C via the first and second gas supply conduits 272A-272C and274A-274C. The gas can pass through the porous membrane 280 and flowthrough the openings 270 of the respective fluid agitator regions266A-266C. The fluid agitator regions 266A-266C can thereby introducegas bubbles 271 into the fluid, which can be guided into the cassette210 by the bubble guide members 256, as illustrated in FIG. 10.

In some embodiments, gas can be provided to the chambers 282A-282C atone or more different pressures and/or flow rates such that gas bubbles271 are produced by the respective fluid agitator regions 266A-266C atdifferent rates, as described above. For example, in the embodimentshown, gas can be supplied to the chamber 282B at a lower flow rate thaneither the chamber 282A or the chamber 282C such that fewer gas bubbles271 are introduced into the fluid at the central fluid agitator region266B than at the fluid agitator regions 266A and 266C. This can resultin a lower density of gas bubbles 271 in the fluid in the fluidreservoir 202 above the fluid agitator region 266B, correspondinggenerally to central regions 217 of the wafers 216, as shown in FIG. 10.As a result, fewer gas bubbles 271 can agitate the fluid adjacent thecentral regions 217 of the wafers 216, which can lower the rate at whichmaterial is etched from the central regions 217. This can result ingreater within-wafer uniformity as compared to conventional wet-etchingsystems by reducing the rate at which material is etched from thecentral regions 217 of the wafers 216. This can also reduce “dishing” ofthe central regions 217 commonly associated with conventionalwet-etching systems, wherein the central regions 217 are etched to agreater extent than the edge portions 222 of the wafers 216 such thatthe material of the edge portions 222 is thicker than the material ofthe central regions 217, resulting in a surface profile resembling adish.

After the wafers 216 have been processed in the fluid reservoir 202, thecassette 210 may be removed from the fluid reservoir 202 and placed in,for example, a rinse tank (such as rinse tank 108 of FIG. 1, and/orlowered into a second fluid reservoir for further processing. In someembodiments, the fluid reservoir can include multiple roller members,multiple fluid agitators, and multiple sets of bubble guide members suchthat the fluid reservoir can receive and process multiple cassettes ofwafers at one time.

Although the steps of the process above are described as occurring in aparticular sequential order, it should be understood that operationfluid of the reservoir assembly 200 need not proceed in the orderdescribed above, but may proceed in any suitable sequence or with somesteps occurring simultaneously, and need not include all of the stepsrecited above.

EXAMPLE 3 Representative Gas Supply System

FIG. 11 is a schematic illustration of a representative gas supplysystem 300 for use with the wet-etching system 100 of FIG. 1. The system300 can include a gas source 302 in fluid communication with a fluidagitator 304, which can be similar to the fluid agitator 206 of FIG. 2.The gas source 302 can be a source of an inert gas, and can be coupledto a two-way valve 306. The two-way valve 306 can be coupled to ahigh-pressure regulator 308, which can comprise a valve configured toreceive gas from the source 302 and limit the pressure of the gas to afirst predetermined pressure. The high-pressure regulator 308 can becoupled to a three-way valve 310, which can allow gas to flow from thehigh-pressure regulator 308 either directly to a coupling element 312,or to pass through a low-pressure regulator 314 prior to flowing to thecoupling element 312. The low-pressure regulator 314 can reduce thepressure of the gas from the first predetermined pressure to a secondpredetermined pressure, which can be lower than the first predeterminedpressure. Thus, the three-way valve 310 can either direct gas from thehigh-pressure regulator to the coupling element 312 directly at thefirst predetermined pressure, or via the low-pressure regulator 314,which can reduce the pressure of the gas to the second predeterminedpressure. In some embodiments, gas can be supplied to the fluid agitator302 at the first predetermined pressure when, for example, fluid is tobe evacuated from chambers such as the chambers 282A-282C in theembodiment of FIG. 2. In some embodiments, gas can be supplied to thefluid agitator 302 at the second predetermined pressure when, forexample, gas bubbles are to be introduced into a fluid in a fluidreservoir in which the fluid agitator 302 is situated during waferprocessing.

The coupling element 312 can be coupled to a flow dividing element 316which can receive gas from the coupling element 312 and divide the gasinto three separate flows. The flow dividing element 316 can beconfigured to provide a separate flow of gas to three adjustable flowmeters 318A-318C. In some embodiments, the adjustable flow meters318A-318C can be configured to regulate or adjust the quantity of gasflowing through the respective flow meters 318A-318C to control, forexample, the number of, size, and/or frequency of bubbles introducedinto the fluid. Information of the flow rate and/or pressure of the gasflowing through each of the flow meters 318A-318C can be provided to acomputer system, which can control the respective flow rates andpressures in accordance with instructions for the particular etchingprocess to be carried out.

Each of the adjustable flow meters 318A-318C, in turn, can be coupled torespective secondary flow dividing elements 320, which can furthersubdivide the gas flows received from the adjustable flow meters318A-318C, respectively, among conduits 322A and 324A, 322B and 324B,and 322C, and 324C, respectively. In some embodiments, the conduits322A-322C and 324A-324C can correspond to the first and second gassupply conduits 272A-272C and 274A-274C of the embodiment of FIG. 2. Theconduits 322A and 324A can be in fluid communication with a fluidagitator region 326A, the conduits 322B and 324B can be in fluidcommunication with a fluid agitator region 326B, and the conduits 322Cand 324C can be in fluid communication with a fluid agitator region326C. Thus, the system 300 can supply gas to the fluid agitator regionsat either the first or second predetermined pressures, and at flow ratesdetermined by the flow meters 318A-318C, as desired.

EXAMPLE 4 Representative Etch Uniformity of Wafers

FIG. 12 illustrates etching profiles of six wafers 402, 404, 406, 408,410, 412 processed in a fluid reservoir assembly similar to the assembly200 of FIG. 2, in which the introduction of gas bubbles was uniformamong the three fluid agitator regions as the wafers were rotated. Thus,the entire surface of each of the wafers 402-412 experienced arelatively uniform flow of gas bubbles. As shown in FIG. 12, this canresult in central portions 402A-412A of the wafers 402-412 experiencinga greater material etch rate than edge portions 402B-412B, resulting ina surface profile wherein the central portions 402A-412A are dished(i.e., lower) relative to the edge portions 402B-412B.

This can also result in varying degrees of surface uniformity among thewafers 402-412 according to their position in the cassette. For example,wafers 402, 404, 406, and 410 in slots 1, 2, 7, and 19, respectively,display relatively high surface uniformity rates of 9.5%, 7.6%, 7.4%,and 8.0%, respectively, despite having been processed together. Incontrast, wafers 408 and 412 in slots 13 and 25, respectively, displayrelatively low surface uniformity rates of 4.6% and 3.9%, respectively.Such dished patterns and disparities in surface uniformity among wafersin different positions in the cassette can be reduced by displacing thewafers from the bottom portion of the cassette, rotating the wafers inthe cassette, and varying the rate at which gas bubbles flow across thecentral portions of the wafers as compared to the edge portions of thewafers during processing.

Displacing the wafers from the bottom portion of the cassette, rotatingthe wafers in the cassette, and varying the rate at which gas bubblesflow across the central portions of the wafers as compared to the edgeportions of the wafers during processing surprisingly significantlyimprove etch uniformity, perhaps due to compensating for varying flowvelocities of the etching fluid at different regions within the fluidreservoir. FIG. 13 illustrates a computer simulation of flow velocitiesof a fluid through a fluid reservoir 500 similar to the fluid reservoir202 of FIG. 2 with respect to a wafer 502 situated in a cassette 504.The lighter regions of FIG. 13 generally indicate a higher fluidvelocity, while the darker regions generally indicate a lower fluidvelocity. As illustrated in FIG. 13, the cassette 504 can cause areduction in flow velocity (i.e., a “shadow”) in regions where the wallsof the cassette 504 are adjacent the wafer 502, such as regions 506 and508. This can result in a lower material etch rate in those regions, asillustrated in FIG. 14. In FIG. 14, the lighter shade of regions 506 and508 indicate that less material has been etched from the surface of thewafer 502 as a result of the lower fluid velocity across the regions506, 508 caused by the proximity of the cassette 504 to the wafer 502.It has been surprisingly discovered by the inventors that displacing thewafers from the bottom portion of the cassette, rotating the wafers inthe cassette, and varying the rate at which gas bubbles flow across thecentral portions of the wafers as compared to the edge portions of thewafers during processing act together to compensate for inconsistentetching rates at different portions of the wafer surface due todifferences in etching fluid velocity and relative location of a waferwithin the cassette, providing surprisingly superior results.

For example, it has been found that certain embodiments of the systemsdescribed herein can provide greatly improved within-wafer (WIW)uniformity, such as WIW uniformities below 5%. Referring to FIG. 15,certain embodiments of the systems described herein have been used toachieve WIW uniformities less than 2% for a 200 mm wafer. As shown inFIG. 15, wafers displaying WIW uniformities of 2.8% prior to processinghave achieved WIW uniformities of 1.8% after processing by embodimentsof the wet-etching systems described herein. In other words, certainembodiments of the systems described herein can process wafers such thatthe resulting processed wafers have a better overall surface uniformitythan before the wafers were processed in the wet-etching system. FIG. 15also illustrates that wafer-to-wafer uniformity, a measure of thevariation of the average planarization of the wafer surface amongstdifferent wafers, can increase after processing in wet-etching systems.

Certain embodiments of the systems described herein are significantlyless expensive than conventional systems. Certain embodiments of thesystems described herein are more compact than conventional systems,requiring less physical space in a production facility such as acleanroom, which adds additional cost savings. Further, certainembodiments of the systems described herein improve etching qualitywhile reducing the quantity of etchant chemicals required, for example,by using the bubbles to agitate the fluid to replenish the etchant atthe surface of the wafers. As a result, such embodiments improvechemical usage by allowing a higher proportion of the etchant in a givenvolume of fluid to interact with the surfaces of the wafers. Further,certain embodiments of the systems described herein can provide greaterthroughput, for example, by allowing at least 25 wafers to be processedconcurrently. Further, certain embodiments of the systems describedherein can be easier to maintain and increase production rates relativeto other known systems.

EXAMPLE 5 Exemplary Wafer Surface Pattern

Certain embodiments of the systems described herein eliminate processingsteps required by conventional wet-etching systems to process certainfeatures. For example, FIG. 16 illustrates a cross section of a wafer600 including a silicon substrate 602, a chemical vapor-deposited (CVD)SiO₂ layer 604, and five features 606, each including a TiW base layer608, a physical vapor-deposited (PVD) gold intermediate layer 610, and aplated gold top layer 612. In some cases, the layers 608 can havethicknesses of 3 kA, the layers 610 can have thicknesses of 1 kA, andthe layers 612 can have thicknesses of 5 μm.

To process a wafer such as wafer 600, many conventional etching systemsrequire two separate tools: a first, wet-etching tool to etch the goldlayers, and a second, dry-etching tool to etch the TiW layers. Thedry-etching tool is often required because use of conventionalwet-etching tools to process TiW features typically results in highlevels of undesirable undercutting of the TiW features. Certainembodiments of the systems disclosed herein can be used to etch both thegold layers and the TiW layers using wet-etching processes available ona single tool. For example, a wafer such as the wafer 600 can first beprocessed in a gold-etching fluid reservoir, then rinsed in a rinsefluid reservoir, then processed in a TiW-etching fluid reservoir. Bydisplacing the wafer 600 from the bottom portion of the cassette,rotating the wafer 600 in the cassette, and varying the rate at whichgas bubbles flow across the central portion of the wafer 600 as comparedto the edge portions of the wafer 600 during processing, certainembodiments of the systems described herein can etch the TiW layer 608between the features 606 with minimal undercutting.

Additional wafer features that may be processed using the systems andmethods described herein include blankets (i.e., relatively flat metalsurfaces) and micro coils.

Representative Computing Environment

In some cases, the systems described herein, such as the wet-etchingsystem 100 and the fluid reservoir assembly 200, can include a computersystem (not shown) for controlling the various operations and processesof the described systems. In some cases, such a computer system cancontrol the operation of any of the devices or systems described herein,such as any of the components of the fluid reservoir assembly 200. Thecomputer system can include one or more processing units and one or morememory units. The processing units can execute computer-executableinstructions, and can be any type of processors. The memory can betangible, and can be volatile memory (e.g., registers, cache, RAM),non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or somecombination of the two, accessible by the processing unit(s). The memorycan store software implementing one or more innovations describedherein, in the form of computer-executable instructions suitable forexecution by the processing unit(s). The computer system can haveadditional features, such as storage, input devices, output devices, andone or more communication connections. An interconnection mechanism asknown to those of ordinary skill in the art, such as a bus, controller,or network may be used to interconnect the components of the computersystem. Typically, operating system software provides an operatingenvironment for other software executing in the computer system, andcoordinates activities of the components of the computer system.

Storage can include removable or non-removable storage, and includesmagnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any othermedium which can be used to store information in a non-transitory wayand which can be accessed within the computer system. The storage storesinstructions for the software implementing one or more innovationsdescribed herein. Input device(s) may be touch input devices such as akeyboard, mouse, pen, or trackball, a voice input device, a scanningdevice, or another device that provides input to the computer system.For video encoding, the input device(s) may be a camera, video card, TVtuner card, or similar device that accepts video input in analog ordigital form, or a CD-ROM or CD-RW that reads video samples into thecomputing system. The output device(s) may include a display, printer,speaker, CD-writer, or another device that provides output from thecomputing system.

The communication connection(s) can enable communication over acommunication medium to another computing entity. The communicationmedium conveys information such as computer-executable instructions,audio or video input or output, or other data in a modulated datasignal. A modulated data signal is a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia can use an electrical, optical, RF, or other carrier.

In view of the many possible embodiments to which the principles of thedisclosure may be applied, it should be recognized that the illustratedembodiments are only representative examples and should not be taken aslimiting the scope of the disclosure. Rather, the scope of thedisclosure is defined by the following claims.

What is claimed is:
 1. An apparatus comprising: a fluid reservoirconfigured to receive a fluid including an etchant and to receive acassette configured to receive a plurality of wafers; and a fluidagitator in fluid communication with the fluid reservoir, the fluidagitator being configured to introduce bubbles into the fluid when thefluid is in the fluid reservoir at a first flow rate to produce a firstflow of bubbles, and to introduce bubbles into the fluid at a secondflow rate that is higher than the first flow rate to produce a secondflow of bubbles; wherein the fluid agitator is further configured suchthat the first flow of bubbles is directed upwardly through a bottomportion of the cassette toward central regions of wafers in thecassette; and wherein the fluid agitator is further configured such thatthe second flow of bubbles is offset from central regions of wafers inthe cassette along the bottom portion of the cassette in a directionacross surfaces of the wafers and toward a side of the cassette suchthat bubbles of the second flow of bubbles flow adjacent edge portionsof wafers in the cassette when the edge portions are adjacent the sideof the cassette.
 2. The apparatus of claim 1, wherein the fluid agitatoris configured such that a flow path of the second flow of bubblesextends upwardly in a direction through the cassette and adjacent theside of the cassette.
 3. The apparatus of claim 1, further comprising aroller member in the fluid reservoir to engage and rotate wafersrelative to the cassette when the cassette is in the fluid reservoir. 4.The apparatus of claim 3, wherein the roller member is configured todisplace wafers from a bottom portion of the cassette when the cassetteis in the fluid reservoir.
 5. The apparatus of claim 1, wherein thefluid agitator is further configured to produce a third flow of bubbleshaving a third flow rate that is higher than the first flow rate.
 6. Theapparatus of claim 5, wherein: the fluid agitator is further configuredto produce the third flow of bubbles such that bubbles of the third flowof bubbles flow adjacent a second side of the cassette that is oppositea first side of the cassette.
 7. The apparatus of claim 1, wherein thefluid agitator is located beneath the cassette when the cassette isreceived in the fluid reservoir.
 8. An apparatus comprising: a fluidreservoir configured to receive a fluid and a cassette, the fluidincluding an etchant, the cassette being configured to receive aplurality of wafers; a fluid agitator in fluid communication with thefluid reservoir, the fluid agitator being configured to introducebubbles into the fluid when the fluid is in the fluid reservoir suchthat bubbles flow upwardly through a bottom portion of the cassette andadjacent central regions of wafers in the cassette at a first flow rate,and bubbles concurrently flow adjacent a side of the cassette at asecond flow rate, the second flow rate being higher than the first flowrate; and a roller member in the fluid reservoir configured to engagewafers in the cassette when the cassette is in the fluid reservoir androtate wafers relative to the cassette such that edge portions of wafersin the cassette pass through a flow path of bubbles introduced into thefluid at the second flow rate, the flow path being offset from centralregions of wafers in the cassette along the bottom portion of thecassette in a direction toward the side of the cassette.
 9. Theapparatus of claim 8, wherein the fluid agitator is configured such thatcentral regions of wafers in the cassette remain free of bubblesintroduced into the fluid at the second flow rate.
 10. The apparatus ofclaim 8, wherein the roller member is configured to displace wafers inthe cassette with respect to a bottom portion of the cassette when thecassette is in the fluid reservoir.
 11. The apparatus of claim 8,wherein: the side of the cassette is a first side of the cassette; andthe fluid agitator is further configured to introduce bubbles into thefluid such that bubbles flow adjacent a second side of the cassette at athird flow rate that is higher than the first flow rate, the second sideof the cassette being opposite the first side of the cassette.
 12. Theapparatus of claim 8, wherein the fluid agitator is configured such thatthe flow path of bubbles introduced into the fluid at the second flowrate extends upwardly in a direction through the cassette.
 13. A method,comprising: removing metal from a wafer surface by: positioning acassette in a fluid reservoir containing a fluid, the cassette includinga plurality of wafers situated therein; rotating wafers in the cassetterelative to the cassette; bubbling gas into the fluid at a first flowrate to produce a first flow of bubbles directed upwardly through abottom portion of the cassette and across central regions of wafers inthe cassette; and bubbling gas into the fluid at a second flow rate toproduce a second flow of bubbles offset from central regions of wafersin the cassette along the bottom portion of the cassette in a directionacross surfaces of the wafers toward a side of the cassette.
 14. Themethod of claim 13, further comprising displacing wafers from a bottomportion of the cassette when the cassette is in the fluid reservoir. 15.The method of claim 14, wherein displacing wafers further comprisespositioning the cassette with respect to a roller member configured torotate wafers in the cassette.
 16. The method of claim 13, whereinrotating wafers in the cassette further comprises rotating wafers in thecassette such that edge portions of wafers in the cassette pass througha flow path of the second flow of bubbles.